Electronic controls for cutting machines



Jan. 28, 1958 R. w. BRADLEY 2,821,670

ELECTRONIC CONTROLS FOR CUTTING MACHINES Filed Feb. 11,- 1955 2 Sheets-Sheet 1 Inventor Robert WB/"ac/Zey By his Attorney Jan.28,'1958 R. w. BRADLEY 2,821,670

ELECTRONIC CONTROLS FOR CUTTING MACHINES Filed Feb. 11, 1955 2 Sheets-Sheet 2 S Inventor Robe/"f Di /Bradley By his Attorney United States PatentO ELECTRONIC CONTROLS FOR CUTTING MACHINES Robert W. Bradley, Marblehead, Mass, assignor to United Shoe Machinery Corporation, Flemington, N. J., a corporation of New Jersey Application February 11, 1955, Serial No. 487,553

1 Claim. (Cl. 317-142) sensitive electronic stroke terminating controls for such presses.

The usual clicking machine as heretofore constructed,

comprises a flat work support, a beam or platen mounted upon a spindle at one side of the support for swinging movement across it, and a power means for reciprocating the beam toward and away from the support to force a freely movable cutting die through sheet material on the i support. In such machines it has been common to provide manually operated control means for the power means arranged so that, upon actuation of the manual control means, the power means is controlled to move the beam, first downwardly through a cutting stroke of predetermined length, and then back to its rest position. Means are also commonly provided for adjusting the length of the stroke and for varying the heightwise position of the beam in its cycle of operation in order to accommodate dies of different heights. The cutting support usually comprises a block of wood or a pad of rubber or other material which is rigid enough to support the sheet material against pressure applied by the platen,

and, at the same time is penetratable by the cutting dies used so that die can be forced through the sheet material and into the block or pad a sufficient distance to insure a complete penetration of the material.

One difliculty which has been experienced heretofore is that the platen must be adjusted to a height above the cutting pad in its rest position for a given length of stroke so that upon operation of the platen the die will be forced completely through the material and into the block and at the same time will not penetrate the block to such an extent that the die will stick. Improper adjustment of the height of the platen for a particular .length of stroke thus may result in the slowing of the cutting operation because of the necessity of prying a stuck die from the block. Penetration of the block also increases the wear thereof and frequently results in unsatisfactory cutting because of the forcing of the material into the block itself.

On the other hand, if the platen does not move downwardly far enough, the die will not be driven completely through the material, resulting in incomplete separation of the blank from the material or in blanks having ragged edges.

The hereinbefore mentioned Patent No. 2,788,070 discloses an improved organization of a cuttingpress in which there is a work support and a platen each embodying a conductive member, the platen being arranged for movement toward and away from the support to engage a die and press it through a work piece on the support, power means for moving the platen, stroke initiating means operable to cause the power means to initiate movement of the platen toward the support, and stroke terminating control means responsive to the formation of an electrical conductance path from the platen member through the die to the support member, to cause said power means to terminate the movement of the platen toward the support.

Where the operation of the stroke terminating control of the organization depends upon direct connection of a power source to a relay switch through the aforesaid path so that the path must carry the relay current, the first contact of the die with the support may not suffice to close the relay, particularly if the conductive material of the support is conductive rubber. Hence the relay response may not be uniformly time related to such first contact but may occur at different stages of die penetration of the work or support, to the detriment of the organization performance.

It is, therefore, an object of the present invention to provide for use in such an organization an improved stroke terminating control having a response which is uniformly time related to a reference condition of a cut, for example, to the first contact between the die and the support even if the resistance of the latter has an appreciable magnitude.

It will be appreciated that the time relation between the formation of such a contact and the optimum time of actual termination of the cutting stroke to insure completion of a cut all around a die will vary, for example, with different materials. This consideration, together with the need for accommodating individual differences in the rate of operation of the mechanical and fluid components of the system requires a means in the stroke terminating control for providing a delay after such 21 reference contact, which delay is variable but which is independent of individual circumstances such as the resistance of the conductance path between the members including the connections thereto.

Accordingly, it is an object of the present invention to provide a stroke terminating control adapted for use in the foregoing organization which control will effectively perform its function with a maximum of sensitivity, stability, and economy.

It is another object of the invention to provide a control adapted for use in such an organization which control affords a variable delay between the first contact of the die with the work support and the control operation, which delay is independent of individual circumstances and which may be reduced to a very low minimum to accommodate inherent system delays.

Yet another object of the present invention is to provide such a control having improved fail-safe features.

To these ends and in accordance with a feature of the present invention there is provided a two-stage safety stroke terminating control employing a relay circuit having a D. C. input stage comprising an electron tube preferably, and as illustrated, a grid-controlled gaseous discharge tube and a normally conducting grid-controlled full-wave A. C. rectifier output stage arranged to be cut 05 upon initiation of a discharge through an input tube to effect relay operation a predetermined time after such initiation. This arrangement prevents initiation of the cutting stroke unless the emission of the output tubes is adequate. The input tube is biased normally non-conductive while means, including connections to the platen and support member, are provided in the grid circuit to change the bias at first contact of the die to. fire the tube.

As illustrated, the initial cut-ofi bias is provided by a source of direct voltage including substantial efiective series resistance. The source is connected across the input electrodes of the tube and across the conductive members of the work support and'platen so that the intermember resistance, which thus loads the source, forms with said series source resistance a voltage divider, where by the effective bias voltage is proportional to the intermember resistance and a reduction thereof below a predetermined value is effective to reduce the bias voltage to the critical level at which the tube becomes conductive, even though the resistance of the path, including the connections, from one member to the other,'has an appreciable magnitude. Accordingly, where said source is "con nected across the platen and support members, contact of a die with both members maybe effective to cause conduction by the tube without any time variation dependent upon the value of the resistance so shunted across the source, provided the value is less than a predetermined value.- This is especially important where the support member comprises material of the nature of conductive rubber which may introduce an appreciable and variable 4V into its lowermost position when the solenoid is energized. The hydraulic system is more completely described in a copending United States application Serial No. 487,634 filed February 11, 1955 in the names of Frank E. Stratten and Fred T. MacKenzie.

Manually operable stroke initiating means for controlling the fiuid-operated motor to initiate a downward stroke of the platen 18 comprises a switchmechanism 42 having an operating handle-3'44 disposed at the front of the platen. in the illustrated position of a switch S2, downward movement of the handle 44 is effective to connect one line 46 of the A. C. supply lines 46, 43 to an intermediate conductor 50, while in the other position of the resistance between the connecting points of the members 7 under difierent die-engaging conditions.

In the control provided by the present invention, a variable time constant circuit is connected in the output circuit ofsaid input stage,- so'that the outputof saidvariable time constant circuit, and consequently its delay function, is isolated by the D. C. input stage from variation with variation of the resistance between "the connections tothe-membe'rs. The use of D. C. plate voltage in the inputstag'e further avoids introducing variations due to the cyclic condition of the alternating-current source.

Other features and advantages of the present invention will be best'understood from the following description taken in connection with the accompanying drawings in which:

Fig. 1 is a diagrammatic representationof apparatus embodying-the presentinvention; and

Fig. 2 is a schematic of a modified embodiment of said invention. I

Referring to Fig. l, the cutting press organization illustrated therein comprises a work support 10 including a conductive work-support'member 12, which may consist of conductive rubber, for supporting work pieces 14 of sheet material, such as leather, fabric or the like to be operated upon by "a freelymovable die 16 to produce blanks. A platen or beam 18, including a metallic striking plate 19 providing a conductive platen member, is mounted upon a vertical post 29 at one side of the support 10 for swinging-movement across it, the platen being arranged for reciprocation toward and away from [the support to force the die 16 through the work piece. For safety reasons, the plate 19 is insulated from the rest of the platen as disclosed in United S tates Letters Patent No. 2,783,838, granted March 5, i957 inthe names-of Roy G. Ericson and Frank E. Stratton.

Power'm'ea'n's for reciprocatingvthe platen 18 are "preferably'fluid operated and'are'illustrated as comprising a piston 22 connected tothe lower end ofthe post and slidably mounted ina'cylinder 24, the cylinder and the piston providing a fluid-operated motor. Control'of-the fluid-operated motor is provided by a valve 26-havingan axially movable valveelement 28. When the valve-element 28 is in its upper position as shown, a lowerport 30 inthe cylinder '24 is connected-to a supply pipe 32 and-an upper port '34-is connected to an exhaust'pipe 36so that the piston 22 is urged upwardly. When the valveelement' 28 is in its lowermost position, the connections-to the ports are reversed so that the piston is urged downwardly.

switch S2, in order to accomplish this connection, not only must the handle 44 be moved downwardly but also a second button 51 on the side of the platen must be depressed, thus requiring both hands of the operator to be above the striking plate 19.when initiatinga cutting stroke.

A starting relay '52 has three normally open sets of contacts, one set,'52a being included in a self-holding circuit for the relay, a second set, 52b, being included in the energizing circuit for the solenoid 40, and the third set 52c, being included in the plate voltage supply circuit of an electronic stroke terminating control. This control, hereinafter described in detail, includes a relay 54 having two sets of normally closed contacts 54a and 54b in'series respectively with the contacts 52a and 52b. An auxiliary relay 56 has three sets of contacts, a normallyopen set 56a'connected between the relay coil and the conductor 50, a normally closed set 56b series-connected in the energizing circuit for the solenoid 40, and a normally closed set 56c series connectedin the energizing circuit for the coil of the relay 52. The coil of relay 56 i's' connected'forenergization upon actuation of a pressure switch 57 or,if a switch S1 is closed, of a limit switch 58, a's'ftirther'disclosed andclaimed in the aforesaid Stratton and MacKenzie application.

Energization of the conductor 50 as aforesaid is eifec- 'tive to energize the relay 52 through the set of contacts "56c; contact'set 52a closes to complete a holding circuit including contacts 560, set 52b closes to energize the solenoid 40 to initiate the cutting stroke, and set 52c closes to supply plate voltage to the stroke terminating control.

The stroke terminating control comprises two thyratrons:60,'62 connected in a two stage relay circuit. The thyratron 60 has input electrodes comprising a control 'grid' 64 and acathode-66. Across the input electrodes is connected an input'circuit comprising a source of direct "currentbias voltage providing substantial effective series resistance, illustrated as a battery 68 in series with a resistor 70, and "a grid current limiting resistor 72. The battery 68 and the resistor 70 are herein considered together as comprisinga source of D. C. bias including substantially effective series resistance although a source having 'equivalent'internal resistancemay be used without a separate resistor. A smoothing condenser 74 is connected across the input electrodes. The source of bias voltage'is connected across the conductive members 19 and'12-of'the platen and support by leads 73 and 75 respectively.

It will be seen that any conductance connected across thebias source as 'a load will operate with its internal resistance, that -is, with the resistor 70, as a voltage divider to redueethe bias voltage on thecontrol grid 64, and that the parameters' o'f the bias source may be adjusted to cause the thyratron 60 to fire at any givenvalue of the shunt conductance, which may conveniently be about 5003000ohms. Thisvalue is suflicient to insure prompt firing of-thethyratrontoreturn the platen should a portioxrof'the' operators hand be caught between the platen and the work support.

Firing of the thyra'tron' 60 produces a voltage across a cathode resistor 76 which voltage is 'applied through -aresistor 38 0f an RC 'timeconstant circuit to initiate the charging of avariable capacitance element 80, which as shown may comprise a bank of condensers and. a selector switch. At the end of a delay period determined by the selected capacity, the voltage at the control electrode 82 of the thyratron 62 rises sutficiently to overcome the negative bias provided in its input circuit by a resistor 84 (connected across the plate voltage supply in series with a resistor 86), thereby firing the thyratron 62.

The thyratron 62 has in its output circuit, in addition to the D. C. source, the coil of the relay 54 which upon energization operates through its upper contacts 54a to break the aforesaid holding circuit to the intermediate conductor 50 and through its lower contacts 54b to break the circuit to the solenoid 40. Accordingly, it will be seen that the solenoid 40 is then deenergized whether the switch 42 is open or closed so that the valve element 28 moves to its upper position to terminate the cutting stroke of the platen and to cause it to be moved upwardly to its rest position. i

It will be seen upon the firing of the thyratron 62 that the relay 54 receives substantially the full plate voltage, a voltage which is preferably more than sufficient to bring in its armature. By employing a plate supply having poor regulation, the initial voltage on the relay may be made considerably higher than its normal operating voltage, to bring in the armature very rapidly without endangering the relay by the imposition of a sustained overcurrent. Accordingly, such mechanical characteristics of the relay as starting friction and the like, which may be variable through the life of the relay, will have minimum deleterious effect upon the timing provided by the control. Hence, I prefer this arrangement to that illustrated in the aforesaid Patent No. 2,788,070 where the time constant circuit comprises a variable capacitance shunted across the relay coil.

An exemplary set of values for the more important components of the circuit is shown in the following table:

Component: Description Tubes 60 and 62 2D2l. Resistor 70 6.8 M.

Bias source 68 18 volts.

Resistor 76 K.

Resistor 78 3.9 M.

Capacitor 80 .0051.5 mfd. variable step-wise.

Resistor 86 1.8 K.

Resistor 84 5.6 K.

B voltage 105 volts.

In operation, employing the stroke terminating control of Fig; 1, the operator will position a work piece 14 on the conductive support member 12, position a die 16 on the work piece and press down the handle 44. The resulting energization of the relay 52 closes the contacts 52b to energize the solenoid and initiate the cutting stroke.

As the platen 18 descends upon the die, the striking plate 19 comes into contact with the die 16 and presses it through the Work piece. As the cutting edge of the die comes into engagement with the support member 12 during the cut, the resistance of the conductance path from the lead 73 through the striking plate, the die 16 and the support member 12 to the lead 75 decreases rapidly, and when it drops below the value required to sustain a nonconductive bias on the thyratron 60, the latter will be fired. Immediately upon such firing, substantially the entire B+ voltage will appear at the cathode of this thyratron and the capacitance element 80 will commence to charge through the resistor 78. When the voltage on the element 80 reaches a value sufficient to overcome the bias in the input circuit of the thyratron 62 provided by its cathode resistor, that tube will fire energizing the relay 54 to open the contacts 54a to break the holding circuit to conductor 50 and to open the contacts 54b to interrupt the energization of the solenoid 40. If the switch 42 is'closed'at this time, the relay 52"will remain energized, continuing the energization of the relay 54. On the other hand if the switch 42 is open, the relay 52 is deenergized by the opening of contacts 54:: to open contacts 52c and so to return the organization to the condition in which it is shown in Fig. 1.

Fig. 2 illustrates an embodiment of the present invention in a two-stage relay circuit in which the input stage is similar to that disclosed in Fig. 1, thus comprising a thyratron having a control grid 102 connected to a source 104 of negative bias voltage comprising a resistor 106. The bias source is connected across the striking plate 19 and the work support member 12' in the same manner as in Fig. 1. The output stage of the control comprises two thyratrons and 112 arranged in a fullwave rectifier circuit in which current normally flows from the ends of the secondary 114 of a transformer 116 alternately through the thyratrons 110 and 112 to their interconnected cathodes and thence through the coil of a relay 118 to a center tap on the secondary 114. The thyratrons 110 and 112 are normally conductive by reason of the connection of their control grids 120 and 122 to the cathodes through grid current limiting resistors 124 and 126 and a resistor 128 connected between the cathodes and the junction of the resistors 124 and 126.

The output circuit of the thyratron 100 may be traced from a source of plate voltage comprising a rectifier connected to one of the supply lines 46 through contacts 132a of a relay 132, through the tube 100 to its cathode, and through a cathode resistor 134 to a lead 136 and back to the supply line 48. The cathode resistor 134 is connected to a time constant circuit comprising a resistor 138 and a variable condenser 140 in such a manner that, when the thyratron 100 is conducting, the voltage drop across the cathode resistor 134 is applied to charge the condenser 140 through the resistor 138 so that the upper plate of the condenser which is connected to the grids of the tubes 110 and 112 is charged negative with respect to the lower plate which is connected to the cathodes of the said tubes. Accordingly, it will be seen that firing of the thyratron 100 operates to cut ofi conduction by the tubes 110 and 112 after an interval determined by the setting of the condenser 140.

In the embodiment of Fig. 2, the cutting stroke is initiated by closure of a hand switch 42 to connect the coil of the relay 132 across the lines 46' and 48. The resultant energization of the relay 132 closes the contacts 132a and 132b respectively to supply plate voltage to the anode of the thyratron 100 and to connect the cathodes of the thyratrons 110 and 112 to the relay 118. If the latter thyratrons are working properly, the relay 118 will then be energized to connect the solenoid 40' across the supply lines 46 and 48' and to complete a holding circuit for the relay 132 around the switch 42. The latter circuits are subject to being broken by energization of an auxiliary relay 54 in response to the closure of a pressure switch 56 in the event of excessive fluid pressure forming in the fluid system.

In operation, employing the control illustrated in Fig. 2, the operator positions the work and die as before described and presses the starting switch 42' to initiate the cutting stroke. When the cutting stroke has progressed to the point where the intermember resistance has been reduced to the level at which the thyratron 100 is caused to fire, the condenser 140 commences to charge until the grids 120, 122 are sufficiently negative with respect to the cathodes to prevent one of the thyratrons 110 and 112 from passing further current. At this time the inductance of the coil of the relay 118 tends to keep current flowing through the other (the last one of the thyratrons 110, 112 which was conducting). At the next half cycle, the sustained discharge of that tube is opposed by the voltage across one half of the secondary 114, so that the voltage across the coil of the relay 118 rises to sustain the discharge, reaching a level higher than its normal operating voltage. Advantage-isgtaken of this fact to discharge theenergyof the solenoid rapidly to provide quickidropout by the provision otgloW-discharge tubes 142 and 144 connectedacross thesolenoid of thetrelay 118. These tubes .areso chosenlthat their breakdown potential is somewhat higher than-the normal operating value of, the relay. lnthecircumstances justdescribed, where conduction ofthe output circuit is interrupted,these-discharge tubes breakdown, quickly to dissipate thecoilenergy for drop-out ofthe relay 118 to deenergize the solenoid 140' for terminating ,the cutting'stroke of the press. .For example, I have employedt-NE48s inthis circuit to efiect a marked reduction in, drop-out time.

Having thus describedv my invention, what I claim as new and desire-to secure by :Letters Patent of the United States is:

Electrical timing apparatus comprising, in combination, a first gaseous ,dischargetube having an anode, a cathode and a control-electrode, an input vcircuit for said tube including'a source of DC. bias voltage effective to maintainsaid tube-normally nonconductive, said biassource including substantial effective series resistance whereby the, bias voltage "may be'reduced to thecritical value by a conductance path of moderate resistance shunted across the source, an output circuit for said tube comprising a D. C. source and a series resistor, a time constant circuit comprising a resistor element anda capacitance element connected in. series' .across'..said "resistor whereby said capacitance element is arrangedfor charging. upon "con duction by said'tube, :tw-o' thyratrons connectedtin a fullwave rectifier .stage, the cathodes and the control grids of said. :thyratrons being connected for negative "biasing by the voltage across said? capacitance elemen't, .a trans former havinga center-tapped secondary, and a relay having :its'coil-connected in series between-the cathodes ofcsaid thyratrons in the center-tap of said secondary, saidprelay .beingthereby arranged normally to beenen gized and tube deenergizjed in response to the initiation of discharge through said discharge tube after an interval determinedbysaid timeconstanttcircuit.

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